@article{HummelObermeierZieretal.2022, author = {Hummel, Sabine and Obermeier, Katharina and Zier, Katja and Krommes, Sandra and Schemme, Michael and Karlinger, Peter}, title = {Analysis of Mechanical Properties Related to Fiber Length of Closed-Loop-Recycled Offcuts of a Thermoplastic Fiber Composites (Organo Sheets)}, series = {Materials}, volume = {15}, journal = {Materials}, number = {11}, pages = {3872}, year = {2022}, abstract = {Increasing demand for energy-efficient means of transport has steadily intensified the trend towards lightweight components. Thermoplastic glass fiber composites (organo sheets) play a major role in the production of functional automotive components. Organo sheets are cut, shaped and functionalized by injection molding to produce hybrid components, such as those used in car door modules. The cutting process produces a considerable amount of production waste, which has thus far been thermally recycled. This study develops a closed mechanical recycling process and analyzes the different steps of the process. The offcuts were shredded using two shredding methods and implemented directly in the injection-molding process. Using tensile tests and impact bending tests, the material properties of the recycled materials were compared with the virgin material. In addition, fiber length degradation via the injection-molding process and the influence of the waterjet-cutting process on the mechanical properties are investigated. Recycled offcuts are both comparable to new material in terms of mechanical properties and usability, and are also economically and ecologically advantageous. Recycling polypropylene waste with glass fiber reinforcement in a closed loop is an effective way to reduce industrial waste in a sustainable and economical production process.}, language = {en} } @article{ObermeierKarlingerSchemmeetal.2022, author = {Obermeier, Frederik and Karlinger, Peter and Schemme, Michael and Altst{\"a}dt, Volker}, title = {Thermoplastic Hybrid Composites with Wood Fibers: Bond Strength of Back-Injected Structures}, series = {Materials}, volume = {15}, journal = {Materials}, number = {7}, pages = {2473}, year = {2022}, abstract = {Due to their lightweight potential and good eco-balance, thermoplastic hybrid composites with natural fiber reinforcement have long been used in the automotive industry. A good alternative to natural fibers is wood fibers, which have similar properties but are also a single-material solution using domestic raw materials. However, there has been hardly any research into wood fibers in thermoplastic back-injected hybrid composites. This article compares the bond strength of an injection molded rib from polypropylene (PP) and wood fibers to different non-wovens. The non-wovens consisted of wood fibers (spruce) or alternatively natural fibers (kenaf, hemp), both with a polypropylene matrix. Pull-off and instrumented puncture impact tests show that, given similar parameters, the natural and wood-fiber-hybrid composites exhibit very similar trends in bond strength. Further tests using viscosity measurements, microscopy, and computed tomography confirm the results. Wood-fiber-reinforced thermoplastic hybrid composites can thus compete with the natural fiber composites in terms of their mechanical behavior and therefore present a good alternative in technical semi-structural applications.}, language = {en} } @article{SchmitzHaupertRuethingetal.2021, author = {Schmitz, Regine and Haupert, Frank and R{\"u}thing, Justus and Sigr{\"u}ner, Michael and Str{\"u}bbe, Nicole}, title = {Tribologische Charakterisierung von Polymerfasern unter Trockenreibung, Mischreibung und Hydrodynamik mittels einer optimierten Pin-on-Disc-Pr{\"u}fmethode}, series = {Tribologie und Schmierungstechnik}, volume = {68}, journal = {Tribologie und Schmierungstechnik}, number = {3-4}, pages = {13 -- 21}, year = {2021}, abstract = {Ausgehend von der herk{\"o}mmlichen Pin-on-Disc-Pr{\"u}fmethodik wurde ein Tribologiepr{\"u}fstand hinsichtlich seiner Leistungsf{\"a}higkeit zur Fasercharakterisierung optimiert und angepasst. Die Methodik wird erl{\"a}utert und erste Anwendungen im Bereich der tribologischen Charakterisierung von Einzelfasern werden vorgestellt. Der Pr{\"u}fungsablauf zur Untersuchung der Polymerfasern, deren Durchmesser nur einige 100 µm betragen, ist so generiert, dass eine Erfassung der Daten als Funktion der Zeit im Bereich von einigen 10 µm bis zu einigen 100 µm Faserverschleiß kontinuierlich w{\"a}hrend der Messung bereits in den ersten Minuten erfolgen kann. Der Pr{\"u}fmodus startet hierbei mit Linienlast und entwickelt sich dynamisch zur Fl{\"a}chenlast durch {\"A}nderung der Auflagefl{\"a}che der Faser w{\"a}hrend der Messung. Es wird gezeigt, dass Einzelfasern hinsichtlich ihrer Reibungs- und Verschleißeigenschaften in unterschiedlichen tribologischen Systemen charakterisiert werden k{\"o}nnen. Die Abh{\"a}ngigkeit der Verschleißraten von Fasermaterial, Oberfl{\"a}chenrauheit der Gegenk{\"o}rper und Schmiermittelraten wird dargestellt.}, language = {de} } @article{SigruenerMuscatStruebbe2021, author = {Sigr{\"u}ner, Michael and Muscat, Dirk and Str{\"u}bbe, Nicole}, title = {Investigation on pull-out behavior and interface critical parameters of polymer fibers embedded in concrete and their correlation with particular fiber properties}, series = {Journal of Applied Polymer Science}, volume = {138}, journal = {Journal of Applied Polymer Science}, number = {28}, pages = {50745}, year = {2021}, abstract = {A crucial problem in concrete engineering is the corrosion of steel reinforcements. Polymer fibers as alternative reinforcement material can prevent corrosion; however, high adhesion to concrete and good fiber mechanics are necessary for polymers to be considered as an alternative reinforcement. This study tested different thermoplastic polymer materials to evaluate their level of adhesion to concrete. The adhesion properties of different self-drawn polymer fibers were analyzed by extracting the fibers from concrete using single fiber pull-out test (SFPT). To determine the adhesion mechanism, different polymer properties were analyzed and correlated to SFPT. Strong evidence was found that the fibers mechanical properties correlate with SFPT. Roughening the fiber surface increases the SFPT results significantly. While highly polar materials can support the adhesion process, a clear correlation could not be found. This study identifies high stiffness and roughness as the crucial properties of polymer fibers used in concrete engineering. If these factors can be engineered into the fiber, polymer fibers can present an alternative to steel in concrete reinforcement.}, language = {en} } @article{ObermeierSchumacherBarthetal.2021, author = {Obermeier, Frederik and Schumacher, Mara and Barth, Simon and Karlinger, Peter and Schemme, Michael and Altst{\"a}dt, Volker}, title = {Verst{\"a}rkung von Polypropylen mit Holzfasern durch Direkt-Compoundierung}, series = {Zeitschrift Kunststofftechnik}, volume = {2021}, journal = {Zeitschrift Kunststofftechnik}, number = {2}, publisher = {Carl Hanser Verlag}, address = {M{\"u}nchen}, pages = {87 -- 111}, year = {2021}, abstract = {Erg{\"a}nzend zum bisherigen Stand der Wissenschaft und Technik wurden in dieser Ver{\"o}ffentlichung Fichtefasern aus einem thermo-mechanischen Aufschlussprozess {\"u}ber einen Spritzgusscompounder mit Polypropylen und Haftvermittler direkt compoundiert. Bei der direkten einstufigen Verarbeitung wurde ein steigender Holzfaseranteil bis 30 Gew.-\% untersucht. Die Charakterisierung der Materialkombinationen erfolgte durch Zugversuche, Melt-Flow-Rate Messungen, Dichtebestimmung, Mikroskopie und Kerbschlagbiegeversuche. Bei steigendem Holzfaseranteil wird eine Steigerung der Zugeigenschaften, der Viskosit{\"a}t und der Dichte festgestellt. Die Kerbschlagz{\"a}higkeit bleibt bei steigendem Holzfaseranteil im Rahmen der Standardabweichung konstant, ist jedoch im Vergleich zum unver{\"a}nderten Grundpolymer geringer.}, language = {de} } @article{VersenErnst2020, author = {Versen, Martin and Ernst, W.}, title = {Row hammer avoidance analysis of DDR3 SDRAM}, series = {Microelectronics Reliability}, journal = {Microelectronics Reliability}, pages = {113744}, year = {2020}, abstract = {A DDR3 SDRAM test setup implemented on the Griffin III test system from HILEVEL Technologies is used to analyse the row hammer bug. Row hammer pattern experiments are compared to standard retention tests for different manufacturing technologies. The row hammer effect is depending on the number of stress activation cycles. The analysis is extended to an avoidance scheme with refreshes similar to the Target Row Refresh scheme for the DDR4 SDRAM technology.}, language = {en} } @article{WohlschlaegerVersen2020, author = {Wohlschl{\"a}ger, Maximilian and Versen, Martin}, title = {Detection of plastics in water based on their fluorescence behavior}, series = {Journal of Sensors and Sensor Systems}, volume = {9}, journal = {Journal of Sensors and Sensor Systems}, number = {2}, pages = {337 -- 343}, year = {2020}, abstract = {Plastic waste is one of the biggest growing factors contributing to environmental pollution. So far there has been no established method to detect and identify plastics in environmental matrices. Thus, a method based on their characteristic fluorescence behavior is used to investigate whether plastics can be detected and identified in tap water under laboratory conditions. The experiments show that the identification of plastics as a function of water depth is possible. As the identification becomes more difficult with higher water depths, investigations with a highly sensitive imaging method were carried out to obtain an areal integration of the fluorescent light and thus better results.}, language = {en} } @article{DechantSeligerKennel2019, author = {Dechant, Eduard and Seliger, Norbert and Kennel, Ralph}, title = {Power cycling and temperature endurance test of a GaN switching cell with substrate integrated chips}, series = {Microelectronics Reliability}, volume = {100-101}, journal = {Microelectronics Reliability}, pages = {113372}, year = {2019}, abstract = {We present a reliability study of a half-bridge switching cell with substrate integrated 650 V GaN HEMTs. Power Cycling Testing with a ΔTj of 100 K has revealed thermo-mechanically induced failures of contact vias after more than 220 kcycles. The via failure mode of contact opening is confirmed by reverse-bias pulsed IV-measurements to be primarily triggered by a ΔTj imposed thermal gradient and not by a high Tj. The chip electrical characteristics, however, remained unaffected during Power Cycling. Furthermore, a High Temperature Storage test at 125 °C for 5000 h has shown no changes in the electrical performance of substrate integrated GaN HEMTs.}, language = {en} } @article{LazarJarre2016, author = {Lazar, Markus and Jarre, F.}, title = {Calibration by Optimization Without Using Derivatives}, series = {Optimization and Engineering}, volume = {2016}, journal = {Optimization and Engineering}, number = {17/4}, publisher = {Springer}, pages = {833 -- 860}, year = {2016}, abstract = {Applications in engineering frequently require the adjustment of certain parameters. While the mathematical laws that determine these parameters often are well understood, due to time limitations in every day industrial life, it is typically not feasible to derive an explicit computational procedure for adjusting the parameters based on some given measurement data. This paper aims at showing that in such situations, direct optimization offers a very simple approach that can be of great help. More precisely, we present a numerical implementation for the local minimization of a smooth function f:Rn→R subject to upper and lower bounds without relying on the knowledge of the derivative of f. In contrast to other direct optimization approaches the algorithm assumes that the function evaluations are fairly cheap and that the rounding errors associated with the function evaluations are small. As an illustration, this algorithm is applied to approximate the solution of a calibration problem arising from an engineering application. The algorithm uses a Quasi-Newton trust region approach adjusting the trust region radius with a line search. The line search is based on a spline function which minimizes a weighted least squares sum of the jumps in its third derivative. The approximate gradients used in the Quasi-Newton approach are computed by central finite differences. A new randomized basis approach is considered to generate finite difference approximations of the gradient which also allow for a curvature correction of the Hessian in addition to the Quasi-Newton update. These concepts are combined with an active set strategy. The implementation is public domain; numerical experiments indicate that the algorithm is well suitable for the calibration problem of measuring instruments that prompted this research. Further preliminary numerical results suggest that an approximate local minimizer of a smooth non-convex function f depending on n≤300 variables can be computed with a number of iterations that grows moderately with n.}, language = {en} } @article{VersenErnstGulati2017, author = {Versen, Martin and Ernst, W. and Gulati, P.}, title = {A row hammer pattern analysis of DDR2 SDRAM}, series = {Microelectronics Reliability}, volume = {76-77}, journal = {Microelectronics Reliability}, pages = {64 -- 67}, year = {2017}, abstract = {A DDR2 SDRAM test setup implemented on the Griffin III ATE test system from HILEVEL Technologies is used to analyse the row hammer bug. Row hammer pattern experiments are compared to standard retention tests. The analysis confirms that the row hammer effect is caused by a charge excitation process depending on the number of stress activation cycles. The stress has to occur in the local neighborhood of the cells under test. Shallow impurity levels support the responsible charge carrier transport process in the used DDR2 SDRAM technology}, language = {en} }